Technical Field
The embodiments herein generally relate to particle detectors and, in particular, to micro ultraviolet (UV) particle detectors.
Description of the Related Art
It is well known that biological materials and organisms fluoresce under UV irradiation. UV light in the 380 nm wavelength range, for example, excites biological metabolic products such as nicotinamide adenine dinucleotide (NADH) and flavins to fluoresce in the visible range. In addition, higher energy UV light; e.g. 260 nm, excites proteins. Since vegetative and spore forms of bacteria contain these biochemicals, the bacteria will also fluoresce when irradiated with UV light. The fluorescent light can be detected using existing light detectors such as a photomultiplier tube (PMT).
Historically, biological aerosol detectors have been based on the exploitation of this phenomenon. These detectors typically use a pump to pull in ambient air containing the biological aerosols into some optical interrogation volume. An irradiative UV light, typically from a laser, light-emitting diode or xenon lamp, is directed to the particles. The bacterial particles thus excited will produce fluorescence light or photons. This light, in turn, travels outwards and hits a PMT or equivalent optical detector and produces an electrical, typically current or voltage, signal. The relevant and absolute magnitude of this detected signal can be used to determine the presence of a bacterial particle.
Consequently, conventional systems detect a fluorescent signal from aerosol in flow-through based designs. In such conventional systems, the aerosol particles are irradiated with UV light and the resultant signal collected and analyzed. This could be accomplished by interrogating the fluorescent signal observed from individual or multiple particles. Conventional systems may also include aerosols that have been impacted onto surfaces and then analyzed as a bulk sample. In such conventional systems, non-specific physical methods such as virtual impaction may be employed based on physical characteristics of the aerosols.
As a result, the interrogated sample would contain contributions from all material having similar physical properties. For example, a 3 μm anthrax aerosol would be collected at the same rate as a 3 μm dirt particle. The contribution of these potential non-threat materials to the observed fluorescent signal limits the application of this approach.
Alternatively, conventional systems can be aqueous-based devices that capture specific biological agent and materials on surfaces for interrogation. Aqueous-based devices are classically executed using an antigen-antibody approach. In such conventional systems, the antibody or similar capture material is placed on a substrate. A solution containing the suspected biological agent or threat material is then placed in contact with the coated substrate. The agent or threat material then attaches to the substrate via the antibody bridge. To detect the suspected biological agent, an additional dye is added to the solution, and the result dye is washed. The resultant dyed material, when excited with a wavelength corresponding to the optical properties of the dye, produces a detectable signal.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for alternative particle detectors for detecting biological agent aerosols.